The present invention relates to imaging systems and, more particularly, to systems capable of imaging hidden or otherwise invisible objects. There exists a large and growing demand for devices that can detect, and display images of, hidden or otherwise invisible objects. Security applications include airport baggage screening and searching for contraband at border crossings. Military applications include detecting hidden weapons and soldiers. Public safety applications include locating victims in burning buildings. Commercial applications include locating pipes, wires or other infrastructure within walls or under roads.
Existing systems, such as x-ray and computerized tomography (CT), capable of imaging hidden objects are large and complex. These systems typically consume large amounts of energy and are typically not portable. Existing portable devices, such as electronic stud sensors, use radar or measurements of dielectric constants to detect hidden objects, however these devices provide essentially binary results, not images of the hidden objects. Existing infrared, ultrasonic and other imaging systems produce adequate images, however, these systems typically operate over relatively small dynamic ranges of signal flux or require re-calibration or relatively slow automatic gain control (AGC) circuits.